driver core: Reject pointless SYNC_STATE_ONLY device links

commit f729a592adb6760013c3e48622a5bf256b992452 upstream.

SYNC_STATE_ONLY device links intentionally allow cycles because cyclic
sync_state() dependencies are valid and necessary.

However a SYNC_STATE_ONLY device link where the consumer and the supplier
are the same device is pointless because the device link would be deleted
as soon as the device probes (because it's also the consumer) and won't
affect when the sync_state() callback is called. It's a waste of CPU cycles
and memory to create this device link. So reject any attempts to create
such a device link.

Fixes: 05ef983e0d65 ("driver core: Add device link support for SYNC_STATE_ONLY flag")
Cc: stable <stable@vger.kernel.org>
Reported-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20210929190549.860541-1-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/base/core.c b/drivers/base/core.c
index a364fe565007c1db5b68816bb8bdef67ff2ce21f..2bc4db5ffe445fdfe1c5b6f6c7eab44b34895f3e 100644 (file)
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -549,7 +549,8 @@ struct device_link *device_link_add(struct device *consumer,
 {
        struct device_link *link;
 
-       if (!consumer || !supplier || flags & ~DL_ADD_VALID_FLAGS ||
+       if (!consumer || !supplier || consumer == supplier ||
+           flags & ~DL_ADD_VALID_FLAGS ||
            (flags & DL_FLAG_STATELESS && flags & DL_MANAGED_LINK_FLAGS) ||
            (flags & DL_FLAG_SYNC_STATE_ONLY &&
             flags != DL_FLAG_SYNC_STATE_ONLY) ||